Oilfield operations, such as surveying, drilling, wireline testing, completions and production, are typically performed to locate and gather valuable downhole fluids. As shown in FIG. 1A, surveys are often performed using acquisition methodologies, such as seismic scanners to generate maps of underground structures. These structures are often analyzed to determine the presence of subterranean assets, such as valuable fluids or minerals. This information is used to assess the underground structures and locate the formations containing the desired subterranean assets. Data collected from the acquisition methodologies may be evaluated and analyzed to determine whether such valuable items are present, and if they are reasonably accessible.
As shown in FIGS. 1B-1D, one or more wellsites may be positioned along the underground structures to gather valuable fluids from the subterranean reservoirs. The wellsites are provided with tools capable of locating and removing hydrocarbons from the subterranean reservoirs. As shown in FIG. 1B, drilling tools are typically advanced from the oil rigs and into the earth along a given path to locate the valuable downhole fluids. During the drilling operation, the drilling tool may perform downhole measurements to investigate downhole conditions. In some cases, as shown in FIG. 1C, the drilling tool is removed and a wireline tool is deployed into the wellbore to perform additional downhole testing.
After the drilling operation is complete, the well may then be prepared for production. As shown in FIG. 1D, wellbore completions equipment is deployed into the wellbore to complete the well in preparation for the production of fluid therethrough. Fluid is then drawn from downhole reservoirs, into the wellbore and flows to the surface. Production facilities are positioned at surface locations to collect the hydrocarbons from the wellsite(s). Fluid drawn from the subterranean reservoir(s) passes to the production facilities via transport mechanisms, such as tubing. Various equipment may be positioned about the oilfield to monitor oilfield parameters and/or to manipulate the oilfield operations.
During the oilfield operations, data is typically collected for analysis and/or monitoring of the oilfield operations. Such data may include, for example, subterranean formation, equipment, historical and/or other data. Data concerning the subterranean formation is collected using a variety of sources. Such formation data may be static or dynamic. Static data relates to formation structure and geological stratigraphy that defines the geological structure of the subterranean formation. Dynamic data relates to fluids flowing through the geologic structures of the subterranean formation. Such static and/or dynamic data may be collected to learn more about the formations and the valuable assets contained therein.
Sources used to collect static data may be seismic tools, such as a seismic truck that sends compression waves into the earth as shown in FIG. 1A. These waves are measured to characterize changes in the density of the geological structure at different depths. This information may be used to generate basic structural maps of the subterranean formation. Other static measurements may be gathered using core sampling and well logging techniques. Core samples are used to take physical specimens of the formation at various depths as shown in FIG. 1B. Well logging involves deployment of a downhole tool into the wellbore to collect various downhole measurements, such as density, resistivity, etc., at various depths. Such well logging may be performed using, for example, the drilling tool of FIG. 1B and/or the wireline tool of FIG. 1C. Once the well is formed and completed, fluid flows to the surface using production tubing as shown in FIG. 1D. As fluid passes to the surface, various dynamic measurements, such as fluid flow rates, pressure, and composition may be monitored. These parameters may be used to determine various characteristics of the subterranean formation.
Sensors may be positioned throughout the oilfield to collect data relating to various oilfield operations. For example, sensors in the wellbore may monitor fluid composition, sensors located along the flow path may monitor flow rates, and sensors at the processing facility may monitor fluids collected. Other sensors may be provided to monitor downhole, surface, equipment or other conditions. The monitored data is often used to make decisions at various locations of the oilfield at various times. Data collected by these sensors may be further analyzed and processed. Data may be collected and used for current or future operations. When used for future operations at the same or other locations, such data may sometimes be referred to as historical data.
The processed data may be used to predict downhole conditions, and make decisions concerning oilfield operations. Such decisions may involve well planning, well targeting, well completions, operating levels, production rates and other configurations. Often this information is used to determine when to drill new wells, re-complete existing wells, or alter wellbore production.
Data from one or more wellbores may be analyzed to plan or predict various outcomes at a given wellbore. In some cases, the data from neighboring wellbores, or wellbores with similar conditions or equipment is used to predict how a well will perform. There are usually a large number of variables and large quantities of data to consider in analyzing wellbore operations. It is, therefore, often useful to model the behavior of the oilfield operation to determine the desired course of action. During the ongoing operations, the operating conditions may need adjustment as conditions change and new information is received.
Techniques have been developed to model the behavior of geological structures, downhole reservoirs, wellbores, surface facilities, as well as other portions of the oilfield operation. Examples of modeling techniques are shown in patent/application/Publication Nos. U.S. Pat. No. 5,992,519, WO2004049216, WO1999064896, U.S. Pat. No. 6,313,837, US20030216897, US20030132934, US20050149307, and US20060197759. Typically, existing modeling techniques have been used to analyze only specific portions of the oilfield operation. More recently, attempts have been made to use more than one model in analyzing certain oilfield operations. See, for example, Patent/Publication Nos. U.S. Pat. No. 6,980,940, WO2004049216, US20040220846, and US 2007-0112547.
Techniques have also been developed to predict and/or plan certain oilfield operations, such as drilling operations. Examples of techniques for generating drilling plans are provided in Publication Nos. US20050236184, US20050211468, US20050228905, US20050209886, and US20050209836. Some drilling techniques involve controlling the drilling operation. Examples of such drilling techniques are shown in Patent Application Nos. GB2392931 and GB2411669. Other drilling techniques seek to provide real-time drilling operations. Examples of techniques purporting to provide real-time drilling are described in U.S. Pat. No. 7,079,952, U.S. Pat. No. 6,266,619, U.S. Pat. No. 5,899,958, U.S. Pat. No. 5,139,094, U.S. Pat. No. 7,003,439, and U.S. Pat. No. 5,680,906.
Despite the development and advancement of modeling techniques in oilfield operations, there is a need to consider the effects of unavailable information and/or uncertain information and/or uncertainty in oilfield parameters on oilfield operations. It is desirable to provide techniques to assess the value of acquiring missing information, and/or assess the value of reducing the uncertainty in information and/or assess the value of reducing the uncertainty in oilfield parameters for decision making support. U.S. application Ser. No. 12/182,890, published under WO2009/018462 shows how this value assessment of the acquired information may change the characteristics of the oilfield operation and propose to selectively consider desired parameters, such as the probable contents of the missing information to be acquired, uncertainty in the acquired information, market uncertainty, private uncertainty, etc. U.S. application Ser. No. 12/182,890 further describes techniques that may be capable of one or more of the following, among others: considering the effect of multivariate, and/or time dependent, and/or continuously distributed, and/or discretely distributed uncertainties, valuing the missing information to be acquired in the future, and providing modeling capability to speed up the value assessment process without jeopardizing the quality of the results.
It now however remains a need for establishing meaningful value-of-information (VoI) metrics for a well test when faced with multiple significant uncertainties. Actually, when faced with multiple critical uncertainties associated with the reservoir and measurement/interpretation, a standard decision tree would become far too cumbersome for practical purposes and may even result in sub-optimal (uneconomic) development decisions from being made because of the discretized nature of the existing decision tree constructs. It therefore remains a need for providing a consistent and functional methodology that can compute meaningful VoI for a well test such that all significant uncertainties are considered.
It is further desirable to consider uncertainty in the well test measurement and/or the interpretation itself. Precisely, it is desirable to provide a means to best establish the optimum well test duration by identifying the time at which maximum marginal VoI from the test is found.